Steroid binding by photoinactivated P. testosteroni will be characterized using the technique of equilibrium dialysis with radiolabeled steroids. The number of binding sites per polypeptide chain and the stability of the steroid-protein complexes formed will be compared with the value of these parameters for the native enzyme. The effects of photoinactivation on selected physical properties of the P. testosteroni isomerase will be evaluated. The following physical properties will be investigated: molecular weight, sedimentation coefficient, circular dichroism spectrum. The remainder of the sequence of the polypeptide chains of the Pseudomonas putida isomerase will be determined. It is expected that this goal will require 2 years to attain. The site of the cysteine residue modified by the II-sensitized photoinactivation of P. putida isomerase reaction will be established by straightforward peptide purification and sequencing technique following the precedent established by our work on the testosteroni isomerase. This work will be closely coupled to completion of the primary structure of the enzyme.